1. Field of the Invention
The present invention concerns a method for operating an x-ray imaging apparatus, and an imaging apparatus that has an x-ray source having a focus and a measurement volume with a central axis around which the focus can be moved. The method is provided to acquire x-ray projections of a measurement subject that is arranged eccentrically relative to the central axis in the measurement volume.
The present invention also concerns a non-transitory data storage medium encoded with programming instructions to implement such a method.
2. Description of the Prior Art
In the acquisition of x-ray projections of a measurement subject to reconstruct at least one image of the measurement subject, particularly in computed tomography, situations can arise in which the measurement subject cannot be arranged in the isocenter of the computed tomography apparatus, i.e., such that the central axis of the measurement volume of the computer tomography apparatus runs through the measurement subject. An example is the examination of a female breast (for radiation therapy planning, for example) that is supported eccentrically relative to the central axis. The challenge in the examination of the female breast is to expose the other body parts of the patient that are not to be examined (for example the other breast of the patient) to as little x-ray radiation as possible.
A known response to this problem is a general reduction of the radiation dose during the acquisition of the x-ray projections, for example by reducing the tube current of the x-ray tube, but this entails the disadvantage of a (normally) reduced image quality of the reconstructed images. Furthermore, body parts that are to be protected are sometimes covered with radiation-absorbing mats, which have the disadvantage of increased image artifacts in the reconstructed images. In the case of a female breast, items known as “breast shields” were and are used. Moreover, an optimally good centering of the body part to be examined in the measurement volume of the computed tomography apparatus always has been and is sought, but this is not always possible due to the dimensions of the patient or of the inside of the patient, and the limited size of the opening of the gantry of the computed tomography apparatus.